Oh well......... ----- Original Message ----- From: "Dan Michaels" To: Sent: Monday, August 27, 2001 9:40 AM Subject: Re: [PIC]: High impedance inputr to PIC A/D > Lawrence Lile wrote: > >DING DING DING DING DING! A WINNER! > > > >Bob, you get the "THE BEST DESIGN HAS ZERO PARTS" award for approaching that > >lofty ideal most closely. What a good idea! > > > > Hi Lawrence, at first I thought so too, regarding Bob's solution. > However, as Harold pointed out, the leakage current out of the pin > - whether configured in analog or digital mode - is going to run into > the high source impedance and ultimately charge the cap to an incorrect > value. Bob's switching method is not going to change this. > > The spec shows [digital] I/O ports have a max leakage of +/-1 uA. > > 1 uA * 2M --> 2v offset, cap or no cap. > > High source impedance only works accurately with truly "tiny" leakage > currents. > > best regards, > - dan michaels > www.oricomtech.com > ======================== > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.